Embodiments of the present invention relate in general to audio frequency amplifiers, and in particular, to audio amplifiers employing systems and methods to increase amplifier performance and fidelity. Embodiments of the present invention further relate to audio amplifiers having alterable harmonic format.
Ever since the invention of the vacuum tube audion by Lee De Forest in 1906, audio frequency amplifiers have been a mainstay of the consumer electronics marketplace. Moreover, audio frequency amplifiers that utilize vacuum tube topologies are still popular and sought after devices, especially in niche markets such as for high end home audio and for use as musical instrument amplifiers, e.g., as utilized to amplify guitar, bass guitar and other electronic instruments.
Many amplifier designs incorporate an output stage that operates in a “Push-Pull” mode. In push-pull mode, output devices are logically divided or otherwise grouped into a pair of output sections that operate in a complimentary fashion. In this regard, the two output sections provide amplification in anti-phase relative to the one another. The anti-phase amplified signals are combined in such a way that the signal currents add and certain distortion signals, such as distortion due to the non-linear characteristic curves of the output devices, subtract from one another. The result is that the pair of output sections can collectively provide more gain than a single output section by itself, and overall distortion is reduced.
Many amplifier designs alternatively incorporate an output stage that operates in a “Single Ended” mode. In single-ended mode, one or more output devices are driven in parallel by a single instance of an input signal having a single phase. As such, the gain of a single-ended amplifier is generally limited to the gain of the output device.
Push-pull amplifiers typically provide greater output power and wider bandwidth compared to single-ended amplifiers. Despite typically exhibiting less output power, single-ended amplifiers are still highly desired and sought after in many applications for their subjectively pleasing harmonic and tonal character, which differs from typical push-pull amplifiers, e.g., due to the distortion canceling byproduct of the push-pull configuration, which can tend to cancel more pleasing even order harmonics.